CHICAGO • Hundreds of protesters marched through downtown Chicago after the city released a video showing a white police officer fatally shooting a black teen 16 times.
Footage from the police car's dashboard-camera showed officer Jason Van Dyke shooting 17-year- old Laquan McDonald even after he had fallen.
While the police union had said Mr McDonald lunged at officers with a knife during the October 2014 encounter, the video showed him moving away from them when Van Dyke fired.
Shortly before the city released the video on Tuesday, Mayor Rahm Emanuel said the officer had violated the "basic standards that bind our community together".
Mr Emanuel said a judgment would also be passed on the city's reaction to the video's release. "Will we use this episode and this moment to build bridges that bring us together as a city, or will we allow it to become a way that erects barriers that tear us apart as a city? It is fine to be passionate, but it is essential that it remain peaceful."
The video's release came about seven hours after Cook County prosecutors charged Van Dyke, 37, with first-degree murder, 13 months after he killed Mr McDonald.
It is the first time in almost 35 years that a city officer has faced such a charge for an on-duty killing, according to the Chicago Tribune.
Hundreds of protesters marched on Tuesday night, shouting, "16 shots! 16 shots!"
Tensions escalated at one point as police got into a shoving match with protesters, who said three people were detained as a result of the scuffle.
"We are just frustrated," said Mr Malcolm London, 22, co-chairman of the Chicago chapter of Black Youth Project 100, by "this city, the police department, the indifference of too many people in this city when black lives are gone, particularly at the brutal hands of police".
The protests in the third-largest city in the United States follow unrest in Ferguson, Missouri, and Baltimore, where black residents died after encounters with police, setting off demonstrations that escalated into violence and looting.
The protests in the third-largest city in the United States follow unrest in Ferguson, Missouri, and Baltimore, where black residents died after encounters with police...
Cook County prosecutors say Van Dyke began firing his 9mm semi-automatic pistol about six seconds after getting out of his squad car. It took Van Dyke up to 15 seconds to empty his weapon, and Mr McDonald was lying on the ground for 13 of those seconds as his body jerked amid puffs of debris as bullets hit the pavement, the prosecutors said.
Van Dyke's lawyer, Mr Daniel Herbert, has said the shooting was justified because the officer feared for his life. Of the eight or more officers at the scene, only Van Dyke fired his gun, Cook County state attorney Anita Alvarez said after Van Dyke was charged on Tuesday.
Police said Mr McDonald, who had PCP in his system, had been behaving erratically and did not obey orders to drop a folding knife.
Cook County Board president Toni Preckwinkle issued a statement contending that "delay and obstruction have prevented justice from being carried out".
She praised Judge Franklin Valderrama for ordering the video's release, but added: "I am dismayed we had to rely on his intervention and that only after his decision was the officer involved charged."
After the judge ordered the release of the graphic footage, Mr Emanuel reversed the city's long- held opposition and urged prosecutors to finish their investigation.
In April, Chicago took the unusual step of paying Mr McDonald's family a US$5 million (S$7 million) settlement. The family had not even filed a lawsuit, according to the Tribune.